Chemical bonding and electronic properties in antimony chalcogenides

The lone-pair antimony chalcogenides are investigated. A detailed qualitative classification of their properties is worked out. We show that the 121Sb Mössbauer isomer shift increases with the covalent character of bonds and with the distortion of the local antimony environment. This is quantitatively explained by a tight-binding band-structure calculation. The lone-pair stereochemical activity also weakens with the forbidden band gap while the conductivity and the metallic character of bonds increase.